Control apparatus



" Npv. 24, 1942. I A E.- KRQGH I CONTROL APPARATUS Filed mg lzz, 1940 4 Sheets-sheaf. 1

I Ill 7 INVENTOR. ANKER E. ROGH Now-Z4, 1942. KRQGH CONTROLAPPARATUS Filed May 22, 194g 4 Sheets-Sheet s" INVENTOR. ANKERY E. KROGH ORNEY Patented Nov. 24,1942- CONTROL APPARATUS Anker E. Krogli, Mount Airy, Pa., assignor to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Application May22, 1941, Serial No. 330,510

14 Claims.

The present invention relates to electrical control apparatus of the proportioning system type in which a normally balanced electrical network or bridge is unbalanced by a controlling condition change, and by its unbalance sets a control motor into operation to effect a corrective control action and to subject said network or bridge to a rebalancing adjustment proportional to the control action. J

The general object of the present invention is to provide an improved control apparatus of the type -mentioned including provisions for separately adjusting the network or bridge impedance in response to variations in cache! two or more related control conditions, and thereby correspondingly actuating the control and rebalanclng motor, and including other motor means for producing a further bridge unbalancing, or compensating effect, dependent on the departure of'one, or more than one, controlling condition from its normal value, and resulting in a further control action of the control motor. I A more specific object of the invention is to provide a simple and effective control system of the kind specified with means for effecting compensating adjustments suitable for the particular conditions, of use, without interfering with the capacity of the system to properly perform its primary functions. a

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advan-- tages, and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment Fig. 5 is a diagrammatic representation of a different embodiment of the invention; and

Fig. Grepresents one modification, and Fig. 7

represents a second modiflcationof a portion of the control apparatus shown in Fig. 1.

In the embodiment of .the invention illustrated in Figs. 1, 2 and 3, A and B comprise control instruments for measuring different work temperatures in a furnace C. The latter, as shown, isan ingot heating soaking pit furnace C, and the instruments'A and B directly measurethe temperatures of thermocouples T and T" respectively responsive to the temperatures at the butt and top ends of an ingot in the soaking pit. The furnace, as conventionally illustrated comprises air inlets C' to a mixing chamber C at opposite sides of the latter. Fuel gas is supplied to the chamber (3 at opposite sides of the latter. Fuel gas is supplied to the chamber 0 by a pipe D including a control valve Q", adjusted by a. motor Q under.

the control of instruments A and B, and control mechanism collectively designated q in. Fig. 1, and shown diagrammatically in Fig. 4. The'mixing chamberopens to the pit chamber through a port C centrally located in the floor or hearth of the pit chamber. The latter ejects waste gas at opposite outlets C In-the conventional type of furnace shown, the air inlet C and the waste gas outlet C at each side of the furnace are connected to a corresponding recuperator (not shown). As

diagrammatically indicated, the roof C of the furnace is removable for the insertion and removal of ingots, and serves as a support for the thermocouple I.

The instruments A and B shown arerecording potentiometer control instruments and may be identical in construction and of known type. The portion of the instrument A of interest herein is shown somewhat diagrammatically in Fig. 2, as

comprising a recorder carriage FA, movable horizontall in one direction or the other, by the rotation of a helically grooved or screw thread shaft F in threaded engagement with-the carriage FA.

As diagrammatically shown, the shaft F is retated by a reversible motor a controlled by the pointer of a galvanometer G, which has one terminal connected to a'contact I-I moved by the.

carriage FA along a potentiometer slide wire resistance H. The latter is energized by a voltage course H, and the thermocouple T is connected between the second terminal of the 'galvanometer G and one end of the potentiometer resistance H. The potentiometer instrument mechanism shown is of the particular form disclosed in my Patent;2,159,97l, granted May 30, 1939.

The control provisions of the instrument A shown in Fig. 2, comprises a so-called control table I cooperating with the'recorder carriage,

FA. The control table I normally occupies a fixed position along the path of movement of the re- 'col'der carriage FA, but may be adjusted along shaft F and in threaded engagement with the table I. A control member F is piv'otalLv connected to the table I to turn about an axis parallel to the shafts F and I'. The part P carries a lateral extension I, which, preferably, is detachably connected to the part P and is formed with an engaging edge which normally rests on roller part F carried by the carriage FA and comprises a horizontal portion I and an inclined portion 1'.

As the recorder carriage FA moves to the left, as seen in the drawings, no movement is given to the control table part P so long as the horizontal edge portion I is in engagement with the roller F, but as the roller F moves away from the left hand end of the edge portion 1, the

control table part F turns down under the action of gravity or other suitable bias force, to the extent permitted by the engagement of the inclined edge portion 1, with the roller F. The

,normal control range of the instrument, in

which its control effect varies with the position of the carriage F, is that required for movement of the roller F" into and out of engagement with the edge portion 1. When its movement to the left carries the roller F out of engagement with the edge portion 1, further down movement of the control table part P is prevented by means hereinafter described.

On a movement of the pen carriage to the right of the position in'which it engages edge 1, part I will be retained in its adiusted position by means described in my above-mentioned patent, and need not be described here.

[control bar J having its underside bearing against the control table part P and prevented from separating from the latter by a guide part I". The control bar J extends between the two stationary endplates E and is connected at its ends to the arms J, each pivotally connected to the adjacent edge plate E by a pivot J coaxial with the pivot for the control table part I. The left arm J is provided with a transverse portion J adapted to engage the upper edge of the ad- Jacent end plate E, and thus arrest the down movement of the control bar J and control table part P gives corresponding movement to athe left, of the edge portion 1.

The up and down movements of the table actuate associated control apparatus located in a lower compartment A of the instrument casing, through a link L having its upper endpivotally connected to an extension J connected to transverse member J and having its lower end pivotally connected to the arm L of a rocking element. The latter comprises a hub portion surrounding a shaft L carried by the adjacent member E. The rocking element also comprises a second arm I to which the upper end of a vertically disposed link M is pivotally connected. The link M is in the form of a round bar or shaft and extends downward through an opening A in the bottom wall of the casing compartment in which 'the potentiometer recording mechanism is normally housed. The lower end of the link M carries an actuating abutment formed by a nut M, which is adjustably secured in place on the link by a lock nut M.

The vertical movements of the abutment M give movements to the actuating element N of ment A". As shown, the actuating element N is a horizontally disposed lever or rock shaft arm formed with a slot N at its free and through which the link M passes. The lever arm N has a gravitational bias for movement in the counter-clockwise direction, as seen in Fig. 2, so that-its slotted end is supported by the abutment nut M and, follows the up and down movements of the latter. The arm N ofthe instrument A is secured to a rock shaft W and when turned gives angular adjustments to a series of depending contact arms a, a, a and a carried by the rock shaft N2 and shown in Figs. 2 and 4. The corresponding contact arms located in the casing compartment of the instrument 3, are shown diagrammatically in Fig. 4 and are there designated b, b, b and b. In Fig. 4, the pen carriage of the instrument B is designated FE and is shown diagrammatically as having a straight line movement and the carriage FA of the instrument A is similarly shown in Fig. 4. In that figure, the dotted line connection between the carriage FA and the contact arms a, a, a ad a, represent the linkage, such as that formed by the elements J, L,

. M and N of Fig. 2, which may be employed to the control apparatus located in the compart- (6 connect the carriage FA and contact arms, and the dotted line connection between the table FB and contact arms b, b, b and b diagrammatically represents the similar linkage of the instrument FB.

This linkage of each instrument should preferably include throttling range adjusting provisions by means of which the extent of the control eifect produced by a given movement of carriage FA or FB. is individually predetermined, because normally the effect resulting from a movement of carriage FA will desirably be difierent from that resulting from an equal movement of carriage FB, To this end, and as will be clear from Fig. 3, the point of attachment of the link. L to lever L is made adjustable toward and away from the axis of shaft L, the extent of up or down movement of link M in response to a given movement of link L depending upon that adjustment. As shown, the link L is attached to a part L" adjustable in slot L" of lever L and clamped in the desired position by screw L". Another slot L is provided in the lever L' on the opposite side of the axis of shaft L from slot L to alternatively ac- 'commodatepart L whereby the direction of a" and a, and contacts b and b respectivelv engage and are adjustable along resistors b" and b". The resistors a and D are at one side, and the resistors b and a" are at the other side of a midresistor ab, and all of said resistors are connected in series between the bridge energizing line conductors I and 2, connected to a suitable source of energizing current. Another resistor 3 forms a second branch of the bridge circuit connected in parallel with the branch including the resistors a"', b, ab, 17 and a circuit, and an equalizing conductor I extends betacts b and b, the resistance removed from the I tween a contact 8 engaging and adjustable along resistor 3, and a contact 1 engaging and adjust able along resistor ab.

The bridge circuit is adapted to be unbalanced by adjustment of resistors a (1 b b or 3, thereby cause a difference in potential between contacts 6 and 1. Such a potential difference causes an unequal division of current flow in opposed solenoid coils 8 and 8 connected in series between the energizing conductors l or 2, and having their adjacent ends connected to conductor 5. The coils 8 and 9 are inductively related to an armature l0, which is moved, on unbalance in the current flows through the coils, toward coil 8 or toward coil 9, depending upon the direction of unbalance. and thereby controls a contact member ll. Contact member H is connected to line conductor 2, and is arranged to engage one or the other of a pair of contacts l2, l3- when armature I is deflected in one dition. Contact I2 is connected to one terminal of the field winding M, of a reversible motor Q and the contact l3 is-connected to one terminal of the second field winding l of the motor, the

opposite terminals of the field windings con-' nected together to line conductor I. Motor Q actuates the valve Q through suitable gearing, and is also operatively connected to' contact 6 along resistor 3, to adjust the latter in the direction to restore the bridge balance when the motor is set into operation by bridge unbalance.

If the apparatus did not extend beyond that' already described, it would eflect control of fuel valve Q jointly from instruments A and B. A movement of the contacts a and a to the left, for example, in response to a decrease in the ingot bottom temperature below its predetermined normal value, will unbalance the bridge.

arm at one side of the contact 1 will be equal to the resistance added to the arm on the opposite side of the contact, whereby equal movements of the contacts in different portions of their range of movement will produce substantially equal valve movements.

A resistor l8 shown in the bridge arm to the left of contact I, is employed to limit the travel of the valve Q, and is adjustable by means of a short circuiting connection including a contact I!) which may beadjusted by a manually adjustable knob 28 connected in a suitable manner to the contact 19. 'The resistance l8 does not significantly upset the symmetry of the circuit just referred to, but any such upsetting efl'ect may be eliminated by placing a similar resistrection or the other from a normal mid posiance and adjustable contact on the opposite side of contact 1 and arranged for operation simultaneously with contact |9.-

In a stable control system such as the one Just described, and without the load compe'n sating'features now to be disclosed, a furnace load change requiring more fuel will tend to make the system maintain atemperature lower than the desired temperature, while a furnace load change requiring less fuel will tend to make .the system maintain a temperature higher than 'the desired value. Electrical load compensating control apparatus is not in itself new, out I have incorporated in Fig. 4 a novel arrangement of such apparatus making practicable the maintenance of more precise temperature control without interference with the other requirements of the control system, than is the case with other control systems including load compensating means, now known. For example, it is desirable, in the control application or use illustrated in Figs. 1-4, to effect a load compensating adjustment in a direction to reduce the fuel supply'if either the ingot butt temperature or the ingot top temperature is too high, butlit is motor Q will adjust the contact 6 to the right and if no further control condition change occurs in the meantime, the valve opening movements of the motor Q will be continued until the movement of the contact '6 rebalances the bridge and equalizes the current flow through the coils 8 and 9, whereupon the contact II will be moved to its midposition in which it engages neither of the contacts i2 and iii. If the drop in ingot bottom temperature is accompanied by a simultaneous ingot top temperature decrease, it will efi'ect a further fuel correction in the same direction, but if the ingot top temperature increases simultaneously with, and in suitable proportion to the decrease in ingot butt temperature, the effects of the two temperature changes will cancel out and no fuel correction will be made. I

The total resistance in the bridge arms including resistors a", b, A" and b, will remain constant notwithstanding adjustment of the resistors as described. This feature is made possible by the arrangement of the contacts and their connection each to one end of the corresponding resistor, so that when more or less of the resistors (1 or b is short circuited, an equal but reverse change in the short circuited portion of the resistor a or 12 is made. Thus on an adjustment of contacts a and a, orof con not desirable to effect a load compensating adjustment in a direction to increase the fuel supply unless both of those temperatures are low.

For purposes of compensating the system for load variations I have shown in Fig.4, electrical load compensating or reset provisions including a reversible motor R coupled tothe contact 1 to adjust the latter, which in the description of the apparatus up to this point, has been considered stationary. Motor R is provided with two fields 2l L and ZIH respectively adapted to rotate the motor armature 2| in a directionto move contact 1 to the left and to the right, thereby increasing or decreasing the fuel supply. The motor R is energized through circuits including contacts a3, a, b and b. Th contacts a and a are deflected by table FA, as are the contacts a and a, in accordance with the variations in v ingot top temperature, and cooperate with stationary contacts a", a. Similarly contacts I) and b are deflected by carriage FB,-as are the contacts I) and b, in accordance with changes in the ingot butt temperature, and cooperate with stationary contacts b", b. When-contacts a a and b b are undefiected, as they will be when both temperatures are normal, no circuitsincluding those contacts will be closed.

When contact I) is deflected to 'the right on a rise in ingot butt temperature, a circuit will be closed to field ZIH from line 2 to switch 22, through the latter when closed, to conductor 23, contacts I) and b, conductor 2|, field 2IH to line I. When contact a is deflected to the 4 i right on a rise in ingot top temperature. a circuit will be-closed for field IIH from line},

' the rightin response to a rise in either the ingot butt temperature, or the ingot top temperature, to thereby effect a closing adjustment of valve Q.

n adeflection of contacts a and b to the left, a circuit is closed from the line conductor 2, contacts a and a", conductor 29, switch 3|, conducto tl, contacts I) and b, field 2IL to line I, but this circuit can be effected only upon deflection of both contacts a and b to the left, and contacts a and b are both deflected to the left only when the inset top and butt temperatures are both low.

The switches 2!, 28 and 30 respectively controlling the circuits above traced, are automatic interrupter switches, which might be made unnecessary in any particular installation by suitably proportioning the motor 2| and its s ar [connection to the contact I, but those switches serve purposes of adiustment adapting the-apparatus to different specific practical requirements, and being closed during relatively iixed-but manually adjustable time periods. Switches/22 and II are mounted on bracket 32 pivoted at It, and the bracket 32 is provided with a roller 3! in engagement with cam 3!. Cam" is driven by a unidirectional motor 3 8 energized from the line wires i and 2, and provided with speed adjustment means including a contact 31. Switch 2' is mounted on a bracket 38 pivoted at II, a roller ll of the bracket being adapted to be engaged by cam 4| driven by a second unidirectional motor 42 also energized from line wires l and Z. The speed of motor 42 is controlled by In adjustable resistor and contact 43, and the speed adjustment devices 31 and 43 are controlled respectively by manual adjusting dials I4 and II, the angular adjustment of said dials determining the time period of closure of switches and their operating means thus form, in effect, means by which the load compensation or reset effect. produced by adjustment of the contact ,I and injected into the coil tive control action,

is proportioned to the durat of departure of the ingot top and ingot butt temperatures from their respective normal values. If it is desired ,2! and ii and 2! respectively. Said switches material of a relatively high electrical resistance,

including a manually adjustable lmobab con-' nected by suitable means ab to a movable contact ab are provided to short circuit more or less of the resistor ab. Preferably, also, the rate and/or extent of movement of motor It may be individually adjusted by means of a speed control adjusting resistor IIA more or less of which is connected in series with motor 2| depending upon the adjustment of a short circuiting con- 15 tact IIB. The latter is adjusted by means of knob 2ID through suitable means 21C.

The general principles of the present invention may be used, in and in connection, with apparatus differing widely in form and purpose from the apparatus shown in Figs. 1-4. Thus, as shown diagrammatically in Fig. 5. by way of example, the invention may be utilized in regulating the supply of steam to the drying roll of a cotton slasher, primarily in response to variations in the moisture content of the yarn passing over the drying rolls, and secondarily in respouse to the actual temperature or steam pressure/in the drying rolls; As those skilled in the art" understand, in the operation of a cotton slasher, it is highly important that the yarn after passing through the sizing bath be dried to the amount required to reduce the moisture content of the yarn to a small predetermined amount.

To this end, the slasher ordinarily comprises a plurality of drying rolls over which the yarn passes in series, and into which steam is passed to heat the rolls. In Fig. 5, B may be assumed to be the final drying roll and 8' an adjacent drying roll of the slasher. Heating steam is supplied to each of the rolls through a steam supply pipe U and branches connected to the hollow axles of the different rolls, at a rate regulated by the adjustment of a valve Q". For the purposes of the present invention, any one of various known arrangements for measuring the moisture content of the yarn may be employed. On the arrangement own, th moisture content of the yarn is dete ined by measuring the electrical resistance of the yarn as it passes between rolls W and W located between the rolls 8 and 8' iournalled in stationary bearings, and the roll W is supported by a lever W'. The latter is biased by a spring W to press the roll W against the yarn passing between it and the roll W with a suitable pressure. To this end, the roll W is grounded, and the roll W is electrically connected through its metallic support W and a conductor ll, to measuring apparatus comprising a potentiometer control instrument AA, which may be generally similar to the instruments A and B previously described. The electrical measuring circuit through which the instrument A and rolls W and W are associated need not be described herein as it may take any of various known forms, one of which is disclosed in my gator-9 application Ber. No. 289,404, filed August As diagrammatically illustrated in Fig. 5. the contacts a", a" and a" are simultaneously ad- Justed by the instrument AA, through a connection shown in dotted lines, to the right or left on a decrease or increase, respectively, in the moisture content of the yarn measured by the instrument AA. The contacts a" and a. engage resistors "A and B, respectively, which are connected in series between the energizing conductors II and II of an electric bridge or control network. As shown, the conductors 50 and ii are energized by their connection to the secondary terminals of a transformer 82. A resistor 58 is connected in series with and between the resistors "A and "B. As shown, the contact a" is connected by a conductor to the right hand end of a resistor Ila. and the contact a." is connected by a conductor II to the left end of the resistor "13. ,In consequence, the adjustment of the contacts a" and a" by the instrument AA does not change the resistance of the circuit branch including A, Is. and B.

The bridge includes two other branches connected in parallel betweenmmfl! conin said conductors between the connections-to the difierent branches. ,One of-thcse lirariches-is formed by reiay'coils l1. and II which are connected in series with one another. A third ciramosi ductors N and, with resistancesll and II tc 'restore trio-yarn humidity to its no m l v m systems shown im ,;m tica11y-.1n F115; ,4-8Ddg5t 1 1! in thateach permits oi-balancing and rebalanccuit branch connectingthe conductors "and II, comprises resistors I .and "Band a resistor II between, and connected. in series with the resistors "A and MB. A contact b" 1 asing the resistor", is adjusted byJadevice -BA responsive to variations in the steam pressure in the drying roll 8. v The device :BA as diagrammatically shown is a Bourdon Variations in the relative magnitudes oi the current fiows'through the relay coils 5] and II,

give corresponding movements to thereby armature II, which then moves a contact. 82 into engagement with one "or the other or the stationary 1 contacts 3 and 64 at oppositesides oi the contact l2, and each out of engagement withthe contact II, in the normal balancedcondition o! the apparatuso .When the'contact .62 enllles the contact 63, as a result or a decrease in the moisture content of the yarn, it energizesaone ing adjustments in accordance ,with the. .movemerits of compensating: and control motoraand -to-cha'nges in eachioiatwoqdiilerent controlling conditions, without-eiiecting such changes in the disposition 1 0! Ithe circuit -.resistance (as to make *theextcnt of the response of the' -controlj'motor j 'tofa g.ven' extent or change in a controlling conditionr substantially diilerent indiii'erent portions of the control range from what it is in another portion of the control range; m in Figs. 4' and?! aremore specifically.

The systems shown in that each system 'includes-fiour 'circuitiadrjusting means, two of which respectively the tw-ocontacts .connectedto the adjacentjends I oi'. the'*two relay-windingsalongthe respective resistors inthe two circuit branches respectively:

field'winding "of the motor QA, which thereupon sheets a correctiveclosing adjustment of the valve 'Q". into engagement with the contact I, itenergizes the field winding Ci of the motor QA which is thereupon actuated to efiect anopening adjustment oi the valve Q". gizing the motor QA comprises a conductor 01 connecting the contact "tonne secondary ter- When the contact I! ismoved The provisions for enermirial otthetransiormer I2, and a conductor Il connecting the second secondary transformer terminal to the opposite ends of the motor windlugs 85 and 66' from those to which the contacts 2 63 and N are connected. Through anoperating connection, shown in dotted lines in Fig. .5; the motor QA, when in operation,'adjustsgcontacts Q and Q along the resistors "A and "B in the direction to rebalan'cethe bridge. The connected end oitherelay coils?" and 58 are connected by a conductor." tothe contact b". in en icement with the resistor I. and to a contactlt in engagement with the resistor .Il. I

The contact R" is adjusted by a compensating motor RA in one direction or the other, under the control of the instrument AA, accordingly as the moisture-contentoi .theyarn is above or below a predetermined normal value. The motor RA is thus made subject to controlby the instrument AA through the contact a'Qand cooperating stationarycontacts'lll and IL. The contact II isconnected toone end otthe field winding '12 and the contact II is connected to one end oi the field winding I3 oi :tl'ieniotor RA.. The other end 01' each field windingv is connected by a conductor 14 to one secondary terminal of transiormer 82, andz the other secondary terminal or the transformer is connected by to thevcontact. a" which i the conductor I8 is adjusted by .the instrument AA. When the moisture content oi theyarn is .ata normal value or within a certain small normal range of values, the contact a" will be between, and out of engagement with either oiithe contacts II and 'H, but on a predetermined decrease crincrease of the moisture 'content' from its normal value, the contact a" will be moved into engagement wlththe contact II or. 'II', respectively, and

the motor RA will then adjust the contact R" to the right or left, respectively, and thereby turengaged bysaid contacts, while each oithe other 'two adjusting means operates to transfer resistancein one or said circuit branches from ,one

. side'tothe other of the contact engaged resistor 'inthatbranch.

From the standpoint'oi control sensitivityin diil'erent portions ottne. control range, there is no significant idi'fierencebetween the ,arrangementzshownln Fig. 4, in .which;,reslstance--is" transferred? by movements .otneach of: thennotor carriagesFA and F8 from'one SldQtOg thQ other of the resistor no in a single branch otthecontrol system, and the arrangement showrrin Fig.

5 in which the instrument as transfers resist: ance .irom one sideto the other of thefcirciiita. branch including the resistor. El, and the control motorQA'transfers resistance from one sideto the other ohthecircuit =branch includingythe U. 2* I o :W ithout suitable--.preventive provisions such a control system as'those shownin Figs. 4 and ii may sometimes become objectionablyunbalanced as a-result; of the operation of its. reset motor,

s after the corresponding. control-;motorj Q3111 restored to the condition in whichthe corre- .sponding control valve or device .shouldbe adadjusted thecorrespondingcontrol valve or other device. into either 01" its two end positions; are

resultot such continued operation of the-reset motor, when the control system issuhseque tly justed back from its end position, thesystem may further. operation of the reset motor-in response .to the controlling conditiondepartureiromnorbe so far out of balancethatthe condition will overswing to the opposite side oi its normal value, beiore the removal of the excessive reset correction will permit thesystem to stabilize. ;.The described overoperation oi the reset motormay-be p evented bymeans operating automatically onthe adjustment 0! the corresponding control valve, into its end position toprevent mal resulting in the adjustment of the valve or device into its end position. For example, the

limit switch mechanism or the controlmotor Q may hep-associated with; the energizing .circuits for the :reset motori'R, so as to prevent the ob--' jectionable excess operation'otthe liittengtl hus g as shown in Fig. 6, the limit switchmechanism Q.ot the motor Q, which operates limit switches Q" and Q between the motor. windings; ll and ll respectively, and the switch contacts cantrolled by the relay armature l0,serve 'alsoto .6 a 2,sos,oa1 I the switch Q respectively connects and disconnects the contact b to' the field winding ML of the reset motor RA; Similarly, the opening and closing of the limit switch Q respectively connects and disconnects the field winding ill! of themotor RA-to the contact'b I Conveniently in some cases, the relayv control switch mechanismincluding contacts |l, i2 and l3 may bereplaced-by a mercury switchY as shown in Fig. 6. Through a suitable connection.

the relay armature it) turns the switch Y clock- Wise or counterclockwise accordingly as the armature I0 is moved to the right or left. When the switch Y is turned clockwise, the mercury within the contact container connects the. right hand pair of terminals extending into the container and thereby connects the field winding I! of the-motor Q""to the supply conductor 2. When the switch Y is turned counterclockwise, the'leit hand pair of terminals extending ,into

the switch container are connected by themercury therein-and the switch Q and the conductor It are then connected tothesupply conductor I. a

As will be apparent, operation 01,. the motor Q into either end position, for: example, that in which the limit switch Q is opened,,-will, by

opening the switch Q,'prevent further operation of thereset motor in the direction inwhich that motor then tends to operate. As soon, however, I

v as a reverse change in the ingot temperature occurs, suiilcient to move the contact b into engagement with the contact b", the resetmotor willbegin to operateinthe direction'tending to check ingot temperature change in the direction which brought the contact b into engagement 40 with the contact I)".

- The same general end attained by the modification of Fig. 6 may also-be attained with the modification of Fig. ,7'inwhich a pair: 01 mercury switches ZL'and ZH are placed in series with 4 the field windings 2IL and-21H respectively of the reset motor R. Each of the switches ZL and "ZH are tilted by the armature II when the latter tilts the switch Y. Switches ZL and ZH are both a closed in the mid position of switch Y,ibutswitch position in the direction to energize the field winding IIH. A

In consequenceywhen the valve Q is adjusted into either of its end positions and-the corresponding adjustment of the contact 6, does not rebalance the bridge, the armature "will hold" Y the corresponding switch ZL or ZH in its open position, and thereby prevent operation ot the reset motor R in the direction tending to increase the existing circuit unbalance, As soon,

however, as the existing departure from normal trol action and adjusting a second of said means oi the control quantity is reversed, the reset motor will start into operation, even thoughthe switch Y has not been returned to its normal position in the meantime. With the arrangement shown in Fig. 7, the reset motor is normally inoperative during periods in which the control motor is' operating. While this results in some interruptions in the operation of the reset motor, when conditions make its operation desirable, such in-':'

terruptions are of negligible practical importance 7 because the control motor is ordinarily in operation only a small traction of the time inwhich the reset motor must .be in: operation to eiiect its retarded compensating adjustments.

' .As those skilled in the art will understand, the present finvention ,is primarily concerned with s the problem oi how'to satisfactorily: minimize the hunting tendency'inevitable in any control system forv a process ,involving time lag, such as the lag in the temperature response oithe ingotsto a variation in the fuel supply tothe furnace shown in Fig. l,.or in the temperature response oiv the slasher drums shown in Fig. 5, to a variation-in the-pressure of the heating steam supplied to those drums. ,The use of the "invention in the control oi a slasher is especially advantageous because itisadapted to care for the special-problem.resulting from the fact that in ordinary practice, the permissible drying drum temperature vari tion is usually quite small, being usually from about 235 F. to about 250 F.

This application is ascontinuationin part of each or my'prior applications, Ser. No. 201,069,

filed April 9, 1938', and issued into Patent 2,285,287 on June 2, 1942, and Ser. No. 202,307, filed April 15, 1938 and issued into Paten 2,285,288 on June 2, 1942.

- While in accordance with the provisions of the statutes, I have illustrated and described the best forms oi my invention'now'known. to me. it will vbe apparent to those skilled in the art, that changes may be made in the form of the I apparatus and modes oi operation specifically illustrated and described'herein, without departing from the spirit of myzinvention asset forth in the appended claims, and will also understand that certain features of my invention maysometimes be used to advantage without a corresponding use of other features. a

Having now described my invention, what I claim as'new and desire to secure by Letters Patent,is: 1

l.-In=an'electric proportioning system, the combination oi'a bridge circuit comprising a'pair of relay windings connected in series to a source of potential 'diflerence and two circuit branches each including a resistor'and connected to said source in parallel with the other branch and with said relay windings, a separate contact means engaging and adjustable along the length of each resistor,'means for transferring resistance in.:one of said branches from .one side to the other or the resistor therein, a second means for transferring resistance in one of said branches from one side to the other'oi'the resistor therein, aconductor connection between the adjacent ends of said relay windings and each of said contact means, a reversible compensating motor energized by and in accordance with the direction of departure 01' at least one oi.a plurality of controlling conditionsirom its normal value and adjustingone of said meansrwhen energized, a

reversible control motor energized'by and in accordance'with differences in the currents flowing in the two relay windings for effecting a conwhen energized, mechanism actuatedby changes in one or said=controlling conditions to adjust a third one of said means, and mechanism actuated by changes in.a..second one oi said controlling conditions to adjust a'iourth one of said means.

2.- In electric proportioning system, the combination .0! abridge :circuit comprising a pair of relay windings connected in series to a source 0! potential'diiierence and two circuit branches each including a resistor and connected to said source in parallel with. the other branch and with said relay windings, mechanism responsive to one control condition fortransferring resistance in one of said branches from one side to the other of the resistor therein, mechanism reone of said controlling conditions from anormal value thereof to effect a corresponding adjustment of one ofsaidcontacts, and a control motor actuated on and in accordance with the difference between the currents flowing through the two relay windings for effecting a control action, and a corresponding adjustment of the other contact. a i

3. In an electric proportioning system, the combinationof a bridge circuit comprising a pair of relay windings connected in series to a source of potential difference and two circuit branches each including a resistor andconnected to said source in parallel with the other branch and withsaid relay windings, a separate contact engaging and adjustable long the length of each of said resistors, mechanism responsive to a change in one controlling condition for transferring resistance in one of said circuit branches from one side to the other of the resistor therein, a compensating motor actuated by and in accordance with the departure of a controlling quantity from a normal value thereof to adjustthe contact engaging the last mentioned resistor along the latter, mechanism responsive to a change in a second controlling condition for adjusting the other of said contacts along the resistor with which it is in engagement, a reversible control motor energized by and in accordance with the differences in the currents flowing in the two relay windings for effecting a control action and for transferring resistance in the branch including the last mentioned resistor from one sideto the other thereof.

4. Automatic control apparatus including an electrical bridge circuit, bridge energizing means, first and second devices, adapted to adjust the impedance of one side of the bridge, third and fourth devices adapted to adjust the impedance of the opposite side of the bridge, means responsive to a first variable condition and connected to adjust said first and third devices in accordance with variations in said condition and thereby proportionately unbalance said bridge while maintaining the total bridge impedance substantially constant, means responsive to a second variable condition related to the first mentioned variable condition, and connectedto adjust said second and fourth devices in accordance with variations in said condition and thereby proportionately unbalance said bridge while maintaining the total bridge impedance substantially constant, a relay connected to said bridge and adapted to respond to bridge unbalance, motor means controlled by said relay and adapted to rebalance said bridge, means adjusted by said motor and adapted to control ofsaid conditions, and additional comv pensating means responsive to one of said conditions. and adapted to unbalanceisaid bridge in 7 accordance withthe difierence between the value of said condition and a predetermined value thereof.

5. Automatic control apparatus including an electrical bridge circuit, bridge energizing means," first and second devices adapted to adjust the impedance of one side of the bridge, third and fourth devices adapted to adjust the impedance of the opposite side of the bridge. means responsive to a first variable condition and connected to adjust said first and third devices in accordance with variations in said condition and thereby proportionately unbalance said bridge while'maintaining the total bridge impedance substantially constant, means responsive to a second variable condition related to the first mentioned varlable condition, and connected to adjust said second and fourth devices in accordance with variations in said condition and thereby proportionately unbalance said bridge while maintaining the total bridge impedance substantially constant, a relay connected to said bridge and adapted to respond to bridge unbalance, motor means controlled by said relay and adapted to rebalance said bridge, means adjusted by said motor and adapted to control both of said conditions, additional means responsive to one of said conditions and adapted to unbalance said bridge in accordance with the diflerence between the value of said condition and a predetermined value thereof, and further additional means responsive to the other of said conditions and adapted to unbalance said'bridge in accordance with the difference between the value'of said other condition and a predetermined value thereof.

6. The combination of claim 5 in which said additional means and said further additional means each comprises electricalcontacts respectively'controlled by said conditions and adapted to energize a reversible electrical motor, the contacts adapted to energizesaid motor in. one direction connected in series, and the contacts adapted to energize said motor in the other direction ccnnectedin parallel.

tions, and a third device responsive to the dif-- ference between. the actual value of either of said conditions and a predetermined value thereof, and adapted to further control said conditions in accordance with said difference,

. and means to eliminate the last mentioned control efiect if either of said conditions exceeds a.

' predetermined value.

8. The combination of claim 7 in which said third device includes electrical contacts selectively energized in accordancewith variations in one condition, and a reversible electrical motor for controlling said condition and energized through said contacts, and in which the eliminating means includes contacts selectively energized in accordance with" variations in the second condition to selectively interrupt 'or complete the energizing circuits closed by the first mentioned contacts. i

9. In a control system," the combination of means responsive to a variable control quantity, control mechanism adjusted by said means on a change in said quantity in a direction selectively dependent on the direction of said change, a reversible electric motor normally actuated by said means on a departure at said quantity irom apredetermined normal value thereof to ei'iect. a compensating adjustment in a direction dependent upon the direction oi departure, a second reversible electrical motor normally actuated by said means to eiiect a control action on each change in said quantity in a direction dependent on the direction oi said change, a limit switch mechanism for interrupting the operation of said second motor on the creation of a consubsequent departure oi said quantity in the mpolite direction irom normal.

10. In a control system, the combination oi a regulator, a reversible electric motor adapted when energized to adjust said regulator, control means ior said motor comprising an electric bridge circuit, first and second adjustable ele- 'a'soaoei controlling conditions to adjust a iourth one oi said means.

12. In an electric proportioning system, the

combination oi a bridge circuit comprising a pair v oi relay windings connected in series to a source oi potential diiierence and two circuit branches each including a resistor and connected to said source in parallel with the other branch and with said relay windings, a separate contact means ments, each adapted to unbalance said bridge circuit on its adjustment, a third adjustable element adapted by its adjustment to neutralize the unbalancing eiiects oi the first and second element adjustments, means responsive to a variable control condition for ei'iecting adjustments oi said first adjustable element, reset means normally operative to eflect delayed adjustments of said second element on and in accordance with the departure oi a control quantityirom a normal value thereof, means through which the operation oi said motor effects a corresponding adjustment of said third element, means actuated by unbalance in said circuit to prevent operation of said reset means and to subject said motor to a control action tending to energize the latter for rebalancing operations, and means actuated by an adjustment oi said regulator oi' predetermined extent in one direction, to prevent energiaation of said motor for Operation to eiiect iurther adjustment oi said regulator in said direction,

engaging and adjustable along the length oi each resistor, means for transferring resistance in one oi said branches from one side to the other oi the resistor therein while maintaining the total resistance of the circuit branch including said resistor constant, a second means ior tramierring resistance in one of said branches irom one side to the. other of the resistor therein, a conductor connection between the adjacent ends of said relay windings and each oi said contact means, a reversible electrical compensating motor energized by and in accordance with the direction of departure oi at least one of a plurality of controlling conditions irom its normal value and adjusting one of said means when energized, a reversible electrical control motor energized by and in accordance with difi'erences in the currents flowing in the two relay windings for eiiecting a control action and adjusting a second oi said means when energized, mechanism actuated by changes in said one oi said controlling conditions to adjust a third one of said means, mechanism actuated by changes in a second one oi said controlling conditions to adjust a iourth one oi said means, a limit switch mechanism ior interrupting the operation of said control motor on the creation of a control efiect oi given magnitude in either direction. and means through which said limit switch mechanism when actuated to interrupt the operation of said control motor also renders said compensating motor inoperative to eiiect iurther adjustment oi said one means in the direction corresponding to the direction oi the previous departure iron: normal resistor. means iortransierring resistance in one oi said branches from one side to the other of the resistor therein while maintaining the total re-- sistance oi the circuit branch including said reaistor constant, a second means 'ior transien'ing resistance in one of said branches from one side to the other oi the resistor therein, a conductor connection between the adjacent ends of said relay windings and each of said contact means,

' a reversible electrical compensating motor energised by and in accordance with the direction of.

oi said branches from one side to the other oi the resistor therein. a second means for transierring resistance in one oi said branches from one side to the other of the resistor therein, a conductor connection between the adjacent ends oi said relay windings and each of said contact means, a reversible compensating motor energized by and in accordance with the direction oi departure of at least one oi a plurality or controlling conditions from its normal value and adjustingone of said means when energized, a reversible control motor energized by and in accordance with diiierences in currents fiowing in the tworelay windings ior eiiecting a control action and adjusting a second of said means when energized, mechanism actuated by changes in said one oi said controlling conditions to adjust a third one of said. means, mechanism actuated by changes in a second one oi said controlling conditions to through which said limit switch mechanismwhen actuated to interrupt the operation 01' said control motor also renders said compensating motor inoperative to efiect further adjustment of said one means in the direction corresponding to the direction of the previous departure from normal 10 of said one controlling condition.

a second device responsive to variations in a second'measurable condition, means "Jointly con-, Q

trolled by said devicesto control said conditions, and a third device responsive to the dliierence between the actual value of either of said condi-j demand a predetermined value thereof and adapted tofurther control said conditions accordance with said diflerence- I ANKER. E. KROGHQ:

a a v 9 14. In a control system, a device'responsive to, variations in the value oi ameasurable condition; 

